Conventionally, as shown in FIG. 7, in a cement manufacturing facility 10 equipped with a fluidized calciner 11, raw material heated through heat exchange with hot gas in a suspension preheater 7 is discharged from a lower-stage cyclone 8 of the suspension preheater 7, part of the heated raw material is dispersively loaded into a rotary kiln exhaust gas duct 9, and the remainder is supplied to a raw material supply chute 12 of the fluidized calciner 11.
In the fluidized calciner 11, air is blown in through a fluidizing air blowing port 13, air chamber 13a, and air dispersion plate 14, forming a fluidizing bed 15. In so doing, the air causes part of the fuel supplied through a pulverized coal supply pipe 16 to combust, makes raw material to be calcined stay in the fluidizing bed 15 for a predetermined period of time, and then causes the raw material to scatter to a free board 17 located above the fluidizing bed 15. Also, hot air from a high-temperature clinker cooler 18 is sucked in a substantially tangential direction through a suction port 19 and the fuel supplied through a pulverized coal supply pipe 16 combusts also on the free board 17. Consequently, the raw material loaded through the upper raw material supply chute 12 and the raw material scattered upward from a surface of the fluidizing bed 15 are calcined efficiently and quickly.
Then, all the calcined raw material enters a separation cyclone 21 by being accompanied by calciner exhaust gas. On the other hand, the raw material dispersively loaded into the rotary kiln exhaust gas duct 9 is also partly calcined by high-temperature rotary kiln exhaust gas and enters the separation cyclone 21 together with the rotary kiln exhaust gas. Furthermore, calcination raw material collected in the separation cyclone 21 is introduced into the rotary kiln 20 through a raw material chute 22.
On the other hand, hot air generated in a clinker cooler 18 is sucked into the rotary kiln 20 and fluidized calciner 11 by suction force of an induction fan 23. However, an amount of suction into the rotary kiln 20 with small draft resistance becomes excessive, and thus cross sectional area is reduced in part of the rotary kiln exhaust gas duct 9, and the amount of suction into the fluidized calciner 11 is adjusted by a damper 24.
Incidentally, in fluidized calciners, it is common practice to use a solid fuel such as coal as a fuel for calcination of cement raw material. Among solid fuels, bituminous coal with good combustion quality is used by being pulverized into fine powder. However, for effective utilization of limited resources, the use of a wide variety of fuels such as coal and oil coke with poor combustion quality is needed.
On the other hand, in the above mentioned conventional fluidized calciner, pulverized coal is conventionally blown into a thick fluidizing bed formed of cement raw material in the bottom from the pulverized coal supply pipe 16 connected to one place on a flank of a furnace body, the pulverized coal tends to flow toward an outlet from the free board 17, with an uneven pulverized coal concentration without being dispersed sufficiently.
Consequently, there is a problem in that oxygen becomes deficient in locations where the concentration of pulverized coal is high while conversely becoming excessive in locations where the concentration is low, causing uneven oxygen consumption and thus incomplete combustion in the furnace, and resulting in a reduced char reaction rate.
In addition, there is a problem in that the char reaction rate of pulverized coal at an outlet of the fluidized calciner 11 becomes low, causing a large amount of unburned carbon to remain in an exhaust gas duct and combust in the preheater 7 and thereby increasing gas temperature in the preheater 7, producing adherents in the cyclone and raw material chute and thereby frequently causing occlusion of a cyclone inlet and outlet and ducts, and obstructing operation.
On the other hand, Patent Literature 1 described below proposes a fluidized calciner for cement raw material, including: a tubular furnace body whose cylinder axis direction corresponds to an up-down direction; an air dispersion plate installed substantially horizontally at a bottom of the furnace body and an air chamber installed under the air dispersion plate; a raw material supply chute adapted to supply raw material on an upper side of the air dispersion plate; a fuel supply nozzle adapted to supply solid fuel to a fluidizing bed on the upper side of the air dispersion plate; and a secondary air duct adapted to supply secondary air (introduced air) to the upper side of the air dispersion plate, wherein the fuel supply nozzle is connected to the furnace body by sloping downward at an angle of 20 degrees or above and being deflected to a tangential side from a centripetal direction.
The above-mentioned conventional fluidized calciner for cement raw material calcinates the raw material through combustion of fuel, but a connecting location of the fuel supply nozzle and the like are based on empirical values and the presence or absence and the like of raw material concentration and gas (especially O2) concentration distributions in the fluidized calciner is not taken into consideration, and consequently there is a problem in that when poorly combustible pulverized coal of coal, coke, and the like is used as a fuel, sufficient calcination cannot be performed and occlusion of ducts may obstruct operation.
Regarding refractories such as the furnace body, there is a problem in that if combustion performance is too high, temperatures around furnace walls will locally become too high, which is highly likely to cause burnout.